Electric motors create mechanical energy from electromagnetic energy. An alternating current (AC) motor generally includes a rotor and a stationary stator. The stationary stator usually has windings of electrical wires which carry an alternating current which produces a rotating magnetic field. Some rotors include ferromagnetic components which respond to the rotating magnetic field generated by the stator, and as the magnetic field of the stator rotates the rotor physically rotates. By coupling the rotor to an output shaft the electromagnetic energy of the AC current is converted to rotational mechanical energy of the output shaft.
Two or more gears can be used to create a mechanical advantage through a gear ratio. There are many ways to arrange gears so that a single rotation of a first gear results in more or less than one rotation of a second gear in the same amount of time. The gear ratio is the ratio of these two rotations. In the case where the second gear rotates less than the first gear the gear combination could be said to provide a gear reduction. In certain applications it is desirable to have an AC motor with a very high gear ratio, where the gear reduction takes place in the smallest possible volume. For example, an actuator that converts many oscillations of the electrical current into a single rotation of the output shaft could have very fine control.
Historically, wobble plate drive mechanisms have seemed a promising route toward a motor having a high gear ratio within a small volume. Examples of such wobble plate drive mechanisms are disclosed in U.S. Pat. Nos. 9,281,736 and 9,124,150. Older systems are disclosed in U.S. Pat. Nos. 2,275,827 and 3,249,776. The disclosures of these and all other publications referenced herein are incorporated by reference in their entirety for all purposes.
In a wobble plate mechanism, one of the gears, for example a rotor gear, nutates around the other gear, for example a stator gear. As used herein, the terms nutate or nutation includes a wobble, a sway, or a circular rocking motion. If the number of gear teeth on the rotor gear and the stator gear are different by one, then such a system would have a gear ratio equal to the number of teeth on the stator gear. In principle, the gear ratios in wobble plate drive mechanisms could be quite high.
The wobble plate drive mechanism disclosed in U.S. Pat. No. 9,281,736 utilizes a stator including three electromagnetic coils distributed circumferentially around a stator axis. These coils are powered by AC currents that are 120 degrees out of phase with each other and create magnetic fields within the coils which are oriented parallel to the stator axis. A wobble plate motor such as this may require an undesirably high peak voltage applied to the coils.